Evidence of a previously unknown Viking king has been discovered in a hoard of silver found by a metal detectorist, stashed in a lead box in a field in Lancashire.

The 201 pieces of silver including beautiful arm rings, worn by Viking warriors, were found on the outskirts of Silverdale, a village near the coast in north Lancashire, by Darren Webster, using the metal detector his wife gave him as a Christmas present. It adds up to more than 1kg of silver, probably stashed for safe keeping around AD900 at a time of wars and power struggles among the Vikings of northern England, and never recovered.

Airdeconut – thought to be the Anglo Saxon coin maker's struggle to get to grips with the Viking name Harthacnut – was found on one of the coins in the hoard.

The Airdeconut coin also reveals that within a generation of the Vikings starting to colonise permanent settlements in Britain in the 870s – instead of coming as summer raiders – their kings had allied themselves to the Christian god. The reverse of the coin has the words DNS – for Dominus – Rex, arranged as a cross.

The hoard is regarded as among the best found this century, and the fact that it was never recovered suggests its owner came to an untimely end.

"It was a considerable sum of money, the price of a reasonable herd of cattle, or a very good herd of sheep," Gareth Williams, a coins expert at the British Museum where the hoard is being studied, said. "One arm ring alone would just buy you an ox."

Webster had collected his son from school, and was heading back to work – but he decided to allow himself a few hours in a field where he had been several times before, but never found anything more exciting than a Tudor half groat.

He hit a strong signal almost immediately, and uncovered a sheet of lead only a few inches down – and was slightly disappointed with his find. The lead proved to be crudely folded into a container, and when he lifted it he released a shower of pieces of silver.

"I knew when I saw the bracelets it had to be Viking," he said. "When I heard later there was one coin that nobody had ever seen before, that was a strange feeling."

The find will go through a treasure inquest next week to determine its value. The reward will be shared between Webster and the land owner. The Museum of Lancaster hopes to raise funds to buy the hoard.

The hoard also had coins minted for Alwaldus, who defected to the Vikings in Northumbria after an unsuccessful attempt to claim the English crown from his considerably better known uncle, Alfred the Great. The Vikings allowed him to call himself a king, but he only survived a few years before dying in battle.

There are also Frankish and Islamic coins, but one of the more intriguing would have been worthless to the original owner. Williams explained that silver coins are often found in Viking hoards, which have been tested by clipping or bending: the scruffy little fake, of copper with the thinnest film of silver almost worn away, shows what they were wary of.

One of the arm rings – usually given by leaders to their warriors in return for services rendered and expected – is particularly unusual, combining Irish, Anglo Saxon and Carolingian style ornament.

Another Viking hoard was found in the next parish in the 1990s, and the site is only about 97km (60 miles) from one of the most famous Viking hoards ever uncovered, the 8,600 pieces of silver, 40kg in total, of the Cuerdale hoard. Staff at the British Museum have been working on the definitive account of its discovery by workmen in 1840, and the contents of the treasure – some closely resembling pieces from the Silverdale hoard – are now within months of publication after a mere 130 years devoted to the task.

The British Museum also announced the most recent results for the treasure finds scheme and the portable antiquities scheme , which encourages voluntary reporting by amateurs of less valuable – but historically priceless – finds. A total of 157,188 antiquities finds were reported, and 1,638 treasure finds in 2009 and 2010,up from 19 reported treasure finds in 1988, an indication of the spectacular increase in reporting since a network of finds officers was established across the country. Treasure finds included a bronze age hoard found near Lewes in East Sussex, evidence of the complex trading networks 3,500 years ago: the objects included gold-foil decoration from northern France, amber beads, which may have come from the Baltic, along with "Sussex loop" bracelets, which have only ever been found within an 80km (50-mile) radius of Brighton.